PhD Theses: Department of Department of Physical Sciences
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Item Effect of microbial biocementation on physicochemical And mechanical properties of mortar Made from portland cements(Daniel Karanja Mutitu, 2020-11) Mutitu, Daniel KaranjaMicroorganisms in soil and water play a significant role in physico-chemical and mechanical properties as well as the durability of building materials. The microorganisms can either contribute to the improvement or deterioration of the materials. Beneficial microorganisms may deposit calcium carbonate in cement mortar or concrete through a process called microbial biocementation. These deposits exhibit binding properties for protecting and consolidating various building materials. Whereas the effect of Bacillus bacteria on fully hardened/cured mortar/concrete is well documented, the effect of such microorganisms on fresh mortar and concrete paste has not been fully investigated. Further, this study examined the microorganisms' biominerals, their chemical composition, and their role in the enhancement of nucleation on cement hydration. The Bacillus species under this study are commonly found in soil/water, are non-pathogenic and are urease active. Bacterial species, Lysinibacillus sphaericus, Sporosarcina pasteurii, and Bacillus megaterium were incorporated separately into the mortar-making mixing water at a concentration of 1.0 × 107 cells/mL. Mortar prisms with 0.5 watercement (w/c) ratio were cast using selected commercial Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC). Some prisms were then cured at room temperature in a microbial solution composed of bacteria, urea, and calcium acetate/calcium chloride, while others were cured in tap water. Lower normal consistency results from microbial mortar pastes than non-microbial pastes in both OPC and PPC were observed. This implied reduced water demand and improved workability. Initial and final setting time were generally lowered, with the OPC paste with Lysinibacillus sphaericus showing the highest reduction. The resultant chemical compounds formed in the mortar were analyzed using Scanning Electron Microscopy (SEM), powder X-ray Diffraction (XRD), and Fourier Transform Infrared (FTIR). Bavenite, Al2Be2Ca4H2O28Si9, and calcite, CaCO3, were found to be the resultant microbial cement hydration products. Compressive and flexural strength gain was observed after the 14th day of curing with the highest compressive and flexural strength gain observed at the 56th day of curing at 19.8 % and 37.0 % respectively for OPC mortars that had Lysinibacillus sphaericus. Rapid accelerated chloride and sulphate penetration tests were performed on the mortar prisms by exposing them to a media of 3.5 % by mass of sodium chloride and sodium sulphate separately for thirty-six hours using a 12V DC power source. The migration diffusion coefficient, Dmig, and apparent diffusivity coefficient, Dapp, for both the Cl1- and SO4 2- for mortar prisms were determined. Dapp was lowered from 3.5340 × 10-10 m2/s to 2.5449 × 10-10 m2/s and from 6.4810 × 10-10 m2/s to 4.5179 × 10-10 m2/s for Cl1- and SO4 2- respectively in PPC mortars that had Bacillus megaterium. After the 28th day of curing, water sorption change was determined across the mortar categories. Water sorption was lowered in the range of 47.8 % to 68.4 %. PPC mortars that had Bacillus megaterium exhibited a water sorptivity coefficient reduction from 0.0289 to 0.0093. The results show that the incorporation of the selected Bacillus species under this study improves the physico-chemical and mechanical properties of the test cements significantlyItem Formulation and Characterization of Prototype Particleboards using selected Crop Residue and Starch from Cassava Peels as a Binder(University of Embu, 2020-11) Warui Kariuki, StephenParticleboards are formulated from lignocellulose material bound with adhesives. Conventional lignocellulose material used is wood particles and adhesive is formaldehyde-based resin. Due to reduction of tree cover, wood has become scarce leading to search for alternative lignocellulose material. Crop residues, as a lignocellulose material, pose disposal problems due to their low biodegradability, hence disposed off mainly by burning. Crop residues are lignocellulose materials of low nutritional value for use as livestock feed. Conventional formaldehyde-based resins hydrolyse in water to form formaldehyde. Epidemiological studies have shown that formaldehyde are carcinogenic and thus harmful. Efforts to reduce the health hazard effects of the formaldehyde-based resins in the particleboard formulation have included, among others, the use of chemical scavengers for formaldehyde and use of an alternative binder. In this study, single layer particleboards were made from cassava peels starch and selected lignocellulose materials. This was done by in-situ chemical oxidation of cassava peels starch and hydrolysis of lignocellulose sources from crop residue followed by condensation polymerization to form composite material. The resultant composite material was moulded to form particleboards. Crop residues used in this study included bagasse, maize straw and rice husks. The residues were sampled from farm and disposal sites in Kirinyaga, Kisumu and Narok Counties. Sawdust was used as a control for the source of lignin. Lignin content was determined following the Klason method. Cassava peel starch adhesive used in this study was analyzed for pH. Na+, Zn2+, Ca2+ and Mg2+ in starch and crop residues were determined using atomic absorption spectroscopy (AAS) and X-ray fluorescence (XRF). The mineralogical content of particleboards was determined using X-ray Diffractometer (XRD). Structure elucidation of compounds in raw materials and particleboards was determined by the use of fourier transform infra- red (FTIR) and nuclear magnetic resonance (NMR). Data obtained from this study were subjected to statistical analysis using Tukey one way analysis of variance (ANOVA). Particleboards were formulated and tested per American Standard for Testing and Materials (ASTM D1037). Average densities for particleboards was between 0.608 gcm- 3 to 0.627 gcm-3, moisture content of 9.51 % to 9.85 %, deionized water absorption (WA) ranged from 61.33 % to 83.87 % and thickness swelling (TS) 18.23 % and 23.43 %. Modulus of Elasticity (MOE) for particleboards was between 2364.2 Nmm-2 to 33329.92 Nmm-2, Modulus of rupture (MOR) ranged from 13.55 Nmm-2 to 14.83 Nmm- 2, internal bonding (IB) ranged from 1.613 Nmm-2 to 2.370 Nmm-2. Elemental analysis for both starch sources and polyphenolic materials for Na+, Zn2+, Ca2+ and Mg2+. Na+ and Zn2+ was less than 1 %. Ca ranged from 4.55 to 13.46 % and Mg ranged from 5.95 to 6.55 %. FTIR and NMR analysis for starch and polyphenolic materials showed that peaks of –OH and -COOH decreased as those of -C-O-C- increased. Particleboards formulated in this study have similar characteristics to medium density fiberboards. They can thus be used for making furniture and doors.Item The Role of Seagrass Meadows in Gazi Bay, Kenya as Carbon Sinks(Edinburgh Napier University, 2017-04) Githaiga, Michael N.Ongoing work on the ‘blue carbon’ has established that vegetated coastal ecosystems – mangroves, seagrasses and tidal marshes – are exceptionally powerful natural carbon sinks. Hence, there are important applied arguments for understanding the role of these ecosystems in climate change mitigation. Many gaps in knowledge remain, with seagrasses in particular being poorly understood. The overall aim of the present study was to understand the role of seagrass meadows of Gazi Bay, Kenya as carbon sinks. The specific objectives of the study were: (i) Carry out a comprehensive review on biomass and productivity studies of seagrasses in Africa. (ii) Estimate the carbon storage in the seagrass meadows of the bay (iii) Investigate the impact of seagrass canopy removal on sediment dynamics and on the benthic faunal communities (iv) Investigate productivity of the dominant seagrass species of the bay. (v) Highlight the implication of the knowledge and how it could be useful in the bundling of the ecosystem services of the seagrass meadows with that of adjacent mangrove ecosystem under the payment for ecosystem services (PES). The review work encountered 32 papers and 8 theses/reports on seagrass biomass and productivity at African sites, with the majority of the studies having been done along the E. African coast; however, there were no published reports of sedimentary Corg from Africa, revealing a major gap in knowledge. Results of carbon storage of the seagrass meadows of Gazi, Bay on biomass and sediment organic carbon (Corg) for the four dominant species, Thalassia hemprichii, Thalasodendron ciliatum, Syringodium isoetifolium and Enhalus acoroides, indicated that sediment organic carbon was highly significantly different between species, range: 160.7 – 233.8 Mg C ha-1 compared to the global range of 115.3 to 829.2 Mg C ha-1 . Vegetated areas in all species had significantly higher sediment Corg compared with un-vegetated areas and revealed a surprising degree of spatial consistency and longevity in relatively small patches of seagrass meadows and bare areas thus demonstrating an exceptionally powerful effect of seagrass on C sequestration. Through a seagrass removal experiment that simulated the impact of seagrass loss on biodiversity and ecosystem functions the study recorded positive elevation change of the sediment in the controls and negative elevation in the treatments with significant effect of treatment and time on surface elevation change. Similarly, there were significant weight losses on clod cards in seagrass removed areas compared to the controls, an indication of the role of seagrasses in the reduction of the speed of water current. Carbon density in surface sediment was significantly higher in the control areas as compared to the treatments while higher litter decay rates were observed in seagrass removed areas than in the controls. Seagrass removal areas had significant decline on the fauna. Productivity estimates of the dominant seagrass species of the bay through a combination of the leaf plastochrone, and ingrowth cores, showed inter-species variability with Thalassia hemprichii recording the highest above and below-ground productivity at 188.6±34.8 g DW m-2 yr-1 and 197.4±108.7 g DW m-2 yr-1 respectively. Knowledge on the role of seagrasses of the bay as carbon sinks is likely to open opportunities for bundling seagrass ecosystem services with that of the contiguous mangrove ecosystem as part of Payment for Ecosystem Services (PES); an approach that makes economic and ecological sense, given the strong connections between the two ecosystems, and could provide a useful buffer against environmental shocks such as sea level rise and increasing storm surges.Item Extraction of Copper Using Chicken Dung and Concentration of Titanium Using Biomass from Ores in Maragwa Location, Tharaka Nithi County(University of Embu, 2020-02) Mutembei, Peterson KugeriaMineral data shows several deposits of copper and titanium minerals in Kenya yet the country continues to import copper and titanium products. In some regions of Tharaka Nithi County, occurs ores that are known to contain both copper and titanium minerals. These minerals have never been earmarked for extraction mainly because the common methods known for extraction are expensive. In addition, the hydrometallurgical or pyrometallurgical process used in copper extraction releases greenhouse gases into the environment. Titanium minerals, on the other hand, are relatively found free of iron minerals. However, titanium extraction from ores must be found mixed with iron minerals. The objective of this study was to extract copper from the ores using impure hydrazones derived from chicken dung and concentrating titanium using ore-laterite-carbonized biomass, carbonized biomass, and froth floatation. Samples were obtained from the selected ore deposits of Maragwa location in Tharaka Nithi County. The samples were obtained at 30 cm depth (level A) and further one-meter depth (level B). Samples obtained were dried at 105oC for 9 hours and later ground to 60.0 meshes (250 microns) using a ball mill. Copper minerals were leached using hydrochloric acid. Titanium in the ore was concentrated using carbonized biomass, ore-laterite-carbonized biomass at 800-900°C, and froth floatation method. The analyses of the minerals for the mineralogical and chemical composition were done using X-ray Diffraction Spectroscopy (XRD), X-ray Fluorescence Spectroscopy (XRF) and Atomic Absorption Spectroscopy (AAS). The chicken dung was characterized using FTIR and MS methods. The copper mineral obtained was chalcopyrite. Copper composition was found to be 4.46%, with a mean of 4.47±0.70% at level A and 4.44±0.60% at level B. The mean rutile composition was found to be 0.92±0.11% with a mean of 0.77±0.16% at level A and 0.86±0.17% at level B. After concentration, rutile improved with a range of 1.0 to 2.5%. Reduction of copper using chlorinated chicken dung at pH above 11 produced copper with purity ranging from 57-85%. The use of iron electrode in acidic media during copper extraction produced Cu with purity ranging from 51-78%. It was found that the aluminium electrode was suitable for monitoring the reduction process of copper from the mixture of ore leachate and chlorinated chicken dung leachate. The copper composition in all deposits was found to be above the cut-off grade of 0.4 to 1.0 percent which is mined in other countries. The reduction of copper using chicken dung generated hydrazones was found to be a good method of copper extraction. This method of copper extraction does not require heavy capital investment since the chicken dung is locally available. The concentration of the ore - laterite using carbonized biomass was also found to be the best method of concentrating titanium from ores. The method is viable because laterite soils (heavily weathered material which is rich in iron oxides or alumina or both) are widely available while biomass is obtained from municipal waste. The experiments were done on the laboratory scale. The study, therefore, recommends a pilot study on large scale copper extraction and titanium concentration using the optimized values.Item Effects of Selected Media on Novel Portland Pozzolana Cement(Kenyatta University, 2009-02) Wachira, Jackson M.Cement is subject to degradation by aggressive media found in the environment. Durability tests are therefore necessary for any cementitious material in a given environment. The work reported in this thesis involved the study of the effects of selected aggressive media on a cement, made from inter-mixing Ordinary Portland Cement (OPC), dried acetylene lime sludge (DALS) and an incinerated mix of reject bricks (BB), spent bleaching earth (SBE) and rice husks. The cement was labelled Portland Combined DALS Cement (PCDC). Initial tests showed that PCDC met the Kenya Standard requirements for Portland Pozzolana cement (PPC). PCDC was subjected to various media which included sea water, distilled water, chloride and sulphate solutions in a laboratory set-up. The experiments were carried alongside OPC, 25 % Pulverised Fuel Ash substituted OPC (OPC + PF A) and commercial Pl'C. The study was carried out in two phases; cement mortar moulded into 100 mm cubes subjected to the media and reinforced mortar cubes subjected to a wet and dry alternate environment of 3.5 % sodium chloride solution. PCDC exhibited continued compressive strength gain in all media except in chloride solutions. PCDC exhibited comparable gain in compressive strength and selected ions intake/leach to PPC in sulphate solutions and distilled water. PCDC exhibited higher strength gain than OPC in distilled water. Except in chloride solutions, PPC exhibited higher strength gain than OPC. In Corrosion tests, the PCDC mortar rebars showed early attainment of active corrosion coupled with higher corrosion rates over a short period of time than OPC as w/c ratio was increased. The PCDC showed a decreased chloride penetration than OPC as w/c and depth of cover increased. PCDC showed the lowest apparent chloride diffusion coefficients. The resistivity of PCDC in the aggressive media suggested that it required greater depths of cover, where reinforcement was to be used, and long term curing to improve on its resistivity. The tests showed that PCDC can be used for general construction work in the tested media in a similar manner to Pl'C,Item Design, Fabrication and Characterization of an appropriate Solar Thermal Electricity Generating System(Jomo Kenyatta University of Agriculture and Technology, 2015-07) Kawira, M.The sun provides an abundant and clean source of energy. However the supply of this energy is periodic following yearly and diurnal cycles, intermittent, unpredictable and it is diffused. Its density is low compared to the energy flux densities found in convectional fossil energy sources like coal or oil. There have been attempts to produce solar thermal power using parabolic trough technology as was demonstrated by Luz Company which built a solar electricity generating station with a power output of 354 MW in USA. Also the largest solar power plants in the world using parabolic trough technology are the Andasol 1 to 3 which are established in Spain. Therefore it was necessary to undertake design and fabrication of a solar thermal electricity generating system consisting of a collector, steam storage system, heat exchanger, turbine and generator as a local solution for power production. The design layouts were done using auto cad. The testing of the steam storage system and the heat exchanger were done using TEMA (Tubular Exchangers Manufacturers Association Standard and ASME (American Society of Mechanical Engineers). Locally produced heat transfer fluids (water, saline solutions, vegetable oils and engine oils) were tested for their suitability in solar power production using guidelines obtained from National Renewable Energy Laboratories. Some of the parameters investigated included mass flow rates, power output, efficiency, steam flow rate, heat absorbed, heat emitted, evaporation ratio, proportion of flash steam, number of heat transfer units among others. The efficiencies of the concentrator when using the heat transfer fluids were in the range of 48.8% to 60.1% for closed collector and in the range of 46.7% to 56.6% for the open collector. The length of complete discharge for the steam storage system ranged from 4.4 hrs to 6.9 hrs. The power output for the heat transfer fluids were in the range of 287.9 W to 467 W. The steam storage was found to have an efficiency of 93.5 % and a thermal capacity of 4.54 kJ. The rate of heat transfer was an average of 68.4 Js-1kg-1 to 46.3 Js-1kg-1. The thermal efficiency for the heat transfer fluids was in the range of 0.85 to 0.66. Available power from the impulse type turbine was 478.4 Watts, isentropic efficiency was 83.5 %, cycle power output was 497.8 W, turbine output was 468.2 W xxii and gear efficiency was 87.9 % and generator efficiency of 86.9 %. The overall efficiency of the system was 34.97%. Coupling of the steam storage system and the heat exchanger increased the capacity of steam storage to 4.15 KJ, at a maximum temperature of 249.5 °C and at a pressure of 7.2 Nm-2. Coupling of the steam storage system and the heat exchanger increased the capacity of steam storage to 4.15 kJ, at maximum temperatures of 249.5 °C and at a pressure of 7.2 Nm-2. A single stage impulse turbine was fabricated which had an average efficiency of 61.6% and a maximum power output of 498 W. The solar thermal characterization and collection was done in solar intensities of the average range 700 Wm-2 to 1100 Wm-2. In Coolidge irrigation facility, a thermocline storage tank has a capacity of 19.8 GJ and operates at a temperature of 288 °C. The thermal capacity of the storage system used in this study was 4.15 kJ and was operating at a temperature of 249.9 °C.Item Studies on Potassium requirements for maize in Nyamira County, Kenya(2015-03) Muthengia, Jackson M.; Kenyanya, OmangaIn Kenya, Maize is a key cereal crop and a major staple food in most Kenyan families. Most maize farmers mainly apply nitrogenious and phosphorous fertilizers to improve on maize yields in the country and Nyamira county in particular. However, acreage yields have been declining yearly despite their use. Application of potassium (K) fertilizers in the regionis limited yet it is the third major nutrient required by maize crop in large quantities for optimum growth and yields. Consequently, it is no longer wise to assume that the soils in the region have enough K levels for good growth and yields. The present study was planned to determine the soils nutrient status and evaluate whether K fertilizers use can play a role to improve maize yield in the region. The field experiments were set and conducted in Gachuba location in Nyamira county. Equilibria K concentrations were determined by flame photometry from filtrate of 2.5g soil in 25ml solutions of various potassium concentrations (0, 25, 50, 75, 100, 125, 150, 175, 200, 225 and 250 mgL-1) after string the mixtures for 24 hours to achieve steady state condition. Adsorption data obtained from the various soil solutions of K were fitted into Langmuir, Freundlich, Temkin and Van Hauy equations. The data fitted Best in Freundlich isotherm model and were farther used to calculate acreage doses. Maize was grown under same doses of nitrogenous and phosphorus fertilizer and ten different doses of potassium in plots of 6m by 5m at two farm sites , that is Gachuba (farm site 1) and Kiang’ede (farm site 2). Maize performance with site and dosage aaplication were determined and growth parameters as well as yield parameters recorded. The study found that maize growth parameters of plant height and stem girth and its yield parameters of ear weight, ear length and grain yields increased steadily as potassium doses were increased and reached their optimum values at potassium doses of 155.84 and 144.76 kg ha-1 giving yields of 3315.27kg ha-1 and 3340.50 kg ha-1 for farm sites 1 and 2 respectively. The concentration levels of available potassium in the soils ranged from 57 to 70 mg kg-1 and with a mean value of 60+- 5.542 mg kg-1. The water soluble potassium ranged from 1.8 to 2.2 mg kg-1 and gave mean of 2.02+-0.16 mg kg-1. Nitric acid extracted potassium had a mean of 149+-2.306 mg kg-1. The mean value energy of replacement, was found as -3572+- 44.98 cal mol-1. The study indicated insufficiency of potassium in the soil for optimum maize production in the region. Also, it established that potassium doses significantly affected concentrations of Phosphorus and nitrogen in the tissues. The findings of this research will create awareness the extent to which potassium has been depleted in soils in the region to both farmers and policy makers and hence appropriate action taken. Also, the information is expected to help extension officers and Farmers to use correct K doses for optimum yields.